1. Field of the Invention
The invention relates to electromagnetically operated clutches and, more particularly, to electromagnetic tooth clutches.
2. Description of the Prior Art
Electromagnetic clutches are generally expensive and bulky because of the number of parts employed and the cost of assembly. As an example, U.S. Pat. No. 3,727,736, owned by the assignee of the present application, discloses an electromagnetic clutch having input and output torque transmitting members. The input torque transmitting member, consisting of three integral subparts, is supported for rotation on the outer race of a ball bearing which, in turn, is supported at its inner race by a sleeve which is brazed to a nonrotating magnet body. U.S. Pat. No. 3,857,468, to Iritono, et al, discloses an electromagnetic clutch having a drive shaft and a driven shaft. On the inner end of the drive shaft is a formed rotary disk. An electromagnet including an energizing coil is mounted to the drive shaft through a bearing. The bearing is secured to the drive shaft against axial movement by a snap ring. These devices have been found to be large and bulky because of the number of parts and placement of the bearing. U.S. Pat. No. 3,559,784, owned by the assignee of the present application, discloses an electromagnetic clutch having a double-row, split-race, thin-section aircraft bearing interconnecting a rotary member with a stationary magnet body. The bearing is held in place by a locking compound. This device has been found to have significant drawbacks because of the large expense of the single source aircraft bearings and the expense of the complex assembly technique.
Electromagnetic tooth clutches as used heretofore have a toothed driving clutch member and a toothed driven clutch member which are moved towards each other upon energization of an electromagnet for engagement of their mutually opposing teeth. A spring disengages the teeth when the electromagnet is de-energized. U.S. Pat. No. 3,669,231, to Schindel, et al., discloses the use of a plurality of springs which extend between an inner flange formed on a jaw member and the heads of a plurality of stop pins which threadably engage corresponding tapped holes symmetrically formed around the axis of a core member. The springs urge the jaw member into an abutting relationship with the core member and disengage the teeth when no electromagnetic force is applied.
U.S. Pat. No. 3,507,374, to Allaben, discloses the use of a compression spring extending between a cup and the head of an elongated stud or guide rod to bias a plunger away from an electromagnetic coil when the electromagnetic coil is de-energized. However, these devices have significant drawbacks when applied to electromagnetic tooth clutches because residual magnetism in the driving and driven clutch members tends to impede the separation of the clutch members, thus, requiring additional biasing force to overcome the metal-to-metal contact of the teeth. When the electromagnet is energized, the electromagnetic force, thus, produced must not only overcome the loss as associated with maintaining a field across an air gap, but also the greater biasing force applied for initial breakaway of the metal-to-metal contact of the teeth.
In U.S. Pat. No. 4,353,450, owned by the assignee of the present application, an electromagnetic clutch is provided with a two-stage disengagement spring for separating the clutch members from one another. In this device, the spring is centrally fastened to one clutch member such that one spring length operates against one radial offset on the armature face while another spring length operates against another radial offset on the armature face. The disengaging springs exert a greater spring force for initial breakaway in order to overcome residual magnetism in the metal-to-metal contact of the mutually opposing teeth and a smaller spring force to further separate the clutch members after initial breakaway. This device has been found to have significant disadvantages. The cost to produce an armature with a pair of radial offsets has been found to be very expensive. In addition, springs have a tendency to move out of position from the radial offsets so that the springs do not exert the proper force upon the armature.
Simplified electromagnetic clutches are also known. As an example, U.S. Pat. No. 3,854,562, to Wilczewski, discloses a compact electromagnetic clutch having a stationary field, a rotor, and an armature. The field is a hollow cylindrical housing made of magnetic material with inner and outer peripheral walls defining an annular recess to receive a plastic bobbin having a toroidal coil and a tubular offset extension through which the coil leads extend and which cooperates with a receiving aperture in the housing to extend therethrough as a lead wire strain relief and an anchor to prevent rotation of the field.
However, none of the above devices provide an inexpensive, compact electromagnetic tooth clutch which is simple to install and has the required operating characteristics.